Apparatus for railway train communication systems



Dec. 15, 1936. P, N, B ART 2,064,643

APPARATUS FOR RAILWAY TRAIN COMMUNICATION SYSTEMS I Filed April 21, 1936 I 25 Roeuz'ng T l Appapazus 1941525] MENTOR av/M S HIS A'ITOFNEY Patented Dec. 15, 1936 PATENT OFFICE APPARATUS FOR RAILWAY TRAIN COMMUNICATION SYSTEMS Paul N. Bossart, Cheswick, Pa, assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application April 21, 1936, Serial No. 75,572 7 Claims. (Cl. 246-8) My invention relates to apparatus for railway train communication systems, and has for an object the provision of novel and improved apparatus for communication between a point on a railway train and a remote point.

I will describe certain forms of apparatus embodying my invention, and will then point out the novel features thereof in claims.

In the accompanying drawing, Fig. 1 is a diagrammatic view of one form of trackway apparatus embodying my invention and wherewith a line conductor positioned on the track ties midway between the track rails is made a channel for transmitting communication current.

Figs. 2 and 3 are diagrammatic views of traincarried communication apparatus which may be used with the trackway apparatus of Fig. 1 and which train-carried apparatus also embodies my invention;

In each of the different views, like reference characters designate similar parts.

A system has been proposed in the United States application for Letters Patent Serial No. 450,135, filed May 6, 1930, by L. O. Grondahl, for Electric train signaling systems, wherewith the track rails in multiple are utilized as a communication channel for transmitting communication current along a railway. My present invention may be considered as an improvement on this Grondahl application.

In Fig. l, the reference characters la and lb designate the track rails of a railway and which rails are formed by insulated rail joints 2 into the usual insulated track sections. Only one full track section AB is disclosed, and it will be understood that the railway is arranged into successive sections similar to the section A-B. Furthermore, it will be understood that. my invention is not limited to a railway track formed into track sections and the track rails may be electrically continuous.

The reference character L designates a line conductor secured to the track ties midway between the track rails la and lb. The line'conductor L may be of any material and size that will assure sufficient mechanical strength and at the same time will provide an efficient conductor for the communication current. The communication current may, for example, be a carrier telephone current of 7500 to 9500 cycles per second. That is, the telephone current may be the upper side band of a carrier of 7000 cycles modulated at voice frequencies of the range of 500 to 2500 cycles per second. The line conductor L may extend the full length of the railway or it may be placed only at selected points. In practicing my invention, I have found that the line conductor L is especially useful at locations where the ballast resistance is relatively low, and a relatively high attenuation of communication current supplied to the track rails occurs. To reduce the characteristic impedance of the line conductor L at the frequency of the communication current and thus increase the amount of communicationcurrent flowing in it in response to an electromotive force induced at any point therein, I provide at selected locations series reactance and leakage, either resistive or capacitive. I also provide at such locations a circuit network to connect the conductor with the track rails to form a ground electrode therefor.

Looking at location A, which is an insulated rail joint location, a circuit network is provided which consists of a resistor 3 connected across the rails at the left-hand side of the insulated rail joints and a resistor t connected across the rails at the right-hand side of the insulated rail joints together with a conductor 5 which joins the mid terminals of the resistors 3 and 4. The conductor 5 is connected with the line conductor L over a resistor 0, and a condenser l is serially interposed in the line conductor. The resistors 3 and 4 are each proportioned so as not to effectively influence the track circuits usually provided for such insulated track sections. I have found that 10 ohms 5 ohms each side of the mid terminal, is satisfactory for such resistors. The condenser l is proportioned to tune out the reactance of the line conductor L at the frequency of communication current and thus reduces its characteristic impedance. The resistor 6 is proportioned to match the characteristic impedance of the line conductor L. With the line conductor L a copper-clad wire of sufiicient size to assure satisfactory mechanical strength and the selected locations about one mile apart, the condenser would be about 0.25 microiarad and the resistor 6 would be about 30 ohms. Since the resistance between the track rails and ground may be of the order of 2 ohms, the circuit network and the rails form a relatively low resistance ground electrode for the line conductor.

At location B, the circuit network is similar to that at location A and consists of two. resistors 8 and 9 connected across the rails at the opposite sides of the insulated rail joints together with a conductor l0 joining the mid terminals of resistors 8 and 9. The line conductor L extends in both directions from location B and two condensers I I and I2 are serially interposed therein. A leakage resistor I3 is connected between the mid terminal of the condensers II and I2 and the conductor I0. At location B all the circuit elements except resistor I3 would be the same as explained at location A. Resistor I 3, which represents the line leakage for the length between shunt elements, is so chosen to reduce as far as possible the characteristic impedance permissible in line conductor L, the limits being set by the maximum attenuation permissible in conductor L and the frequency distortion permissible. Suitable values might be a current attenuation of four to one per mile, and an amplitude distortion of two to one throughout the desired frequency range.

At location C, which is not an insulated rail joint location, a resistor I4 is connected across the track rails, two condensers I 5 and I6 are serially interposed in the line conductor L and the mid terminal of resistor I4 is connected with the mid terminal of the condensers over a leakage resistor H. In the case the distance between the locations B and C is about the same as the distance between the locations A and B, say, for example, about one mile, the resistor I4 would be about 20 ohms while the condensers I5 and I6 and the resistor I 1 would be approximately the same as the corresponding parts at location B. As explained hereinbefore, the line conductor L may extend along any desired stretch of the railway and it will be understood that connections between the line conductor and the rails at selected points would be provided along its entire length. The manner wherewith the line conductor L functions as a communication channel will appear hereinafter.

Figs. 2 and 3 disclose train-carried communication equipment that may be used with the trackwa; apparatus of Fig. 1. The train-carried equipment may be mounted on any desired vehicle of a railway train such, for example, as the caboose on a freight train, and which vehicle is here indicated by the reference character V. The communication equipment ordinarily consists of transmitting apparatus, receiving apparatus, switching apparatus, a sending circuit and a receiving circuit. The transmitting apparatus is capable of supplying communication current which may be a carrier telephone current such as assumed hereinbefore. The receiving apparatus is responsive to such communication current and the switching apparatus is effective either manually or automatically to selectively render the transmitting apparatus or the receiving apparatus active. In Fig. 2, the transmitting apparatus TA, receiving apparatus RA, and switching apparatus SA are each shown conventionally for the sake of simplicity since the specific structures for these apparatuses form. no part of my present invention and they may be any one of several well known types. It is deemed sufficient for the present application to point out that the transmitting apparatus TA when made active supplies communication current to the primary winding I8 of a transformer T, the secondary winding I9 of which is interposed in a sending circuit. As here shown, a sending circuit may be traced from the righthand terminal of the secondary winding I9 over conductor 20 to a point above the roof of the vehicle V, lengthwise along the roof by conductor 2|, downward by conductor 22 to the truck wheel 23 at the left-hand end of vehicle V, thence through the track rails in multiple to the truck wheel 24 at the right-hand end of the vehicle and conductor 25 to the opposite and left-hand terminal of the secondary winding I9. Communication current flowing along the track rails between wheels 23 and 24 creates an electromotive force which causes communication current toflow in the track rails in multiple from the vehicle and return through the ground in the manner described in the aforecited Grondahl application.

This sending circuit on the vehicle V also induces an electromotive force in the line conductor L due to the inductive relationship between the sending circuit and the line conductor. The electromotive force induced in line conductor L causes communication current to flow in the line conductor from the point of induction through the circuit network and rail to ground resistance at the locations to one side of the point of induction, thence by the ground path, rail to ground resistance and circuit networks to the line conductor at the locations to the other side of the point of induction. The current how in the line conductor channel is relatively large since the characteristic impedance and shunt leakage of the line conductor is reduced by virtue of the reactance associated therewith. Since the distributed conductance of the line conductor L to ground is relatively high, the attenuation of the communication current is relatively low and is largely determined by the reactance and lumped leakage associated with the line conductors. Consequently, the sending circuit of vehicle V is effective to cause communication current to flow in two channels one of which includes the track rails in multiple and ground, and the other of which includes the line conductor L and ground and substantially no mutual induction between these two channels takes place.

It is to be pointed out that the track rails Ia and lb form a return path for current induced in the line conductor L. For example, a circuit may be traced from the line conductor L in the section AB through condenser I, resistor 6, conductor 5 to the mid terminal of resistor 4, the two portions of resistor 4 to rails la and lb, rails Ia and lb, the two portions of resistor 8 to its mid terminal, conductor I0, resistor I3, condenser I I and to line conductor L. The impedance of the rails Ia and lb to the communication current is high and the current flowing over the rails as a return path for this circuit just traced is negligible. The ground path, however, forms a relatively low impedance return path for the current induced in the line conductor L.

The receiving apparatus RA of vehicle V is connected with a receiving circuit which includes two inductors HC and LC. This receiving circuit may be traced from the upper left-hand terminal of apparatus RA over conductor 26, inductor HC, conductor 21, inductor LC, and conductor 28 to the lower left-hand terminal of apparatus RA. The inductors HC and LC may take different forms, and, as here shown, are air core coils of relatively large central area and which are disposed in a vertical plane. The inductor HC is mounted on the vehicle V relatively high above the vehicle body to link a horizontal magnetic field transverse to the track rails. I have found that inductor I-IC mounted to one side of the cupola and on the roof of a caboose gives relatively large mutual induction to the track rails Furthermore, the noise energy picked up by an inductor mounted high on a vehicle is relatively low, that is, the high inductor has a better signal to noise energy ratio than an inductor mounted close to the track rails. It appears that this noise is, to a large degree, due to minute electric currents which flow through the rails because of the motion of the wheels on them. The inductor LC is preferably mounted under the center of the vehicle as shown in Fig. 2 and midway between the track rails as shown in Fig, 3. The inductor LC ispositioned as low as possible, but above the top of the track rails sufiicient to provide satisfactory clearance with trackway fixtures. This position of inductor LC gives large mutual induction to the line conductor L. Inductor LC is also as far removed as possible from the vehicle wheels and the noise energy produced by the rolling contactof the wheels on the rails is reduced as much as possible. Two advantages result from this particular location of inductor LC. First, it is asfar separated as possible from the vehicle wheels and the signal to noise energy ratio is low; and, second, it is near to the line conductor located midway between the rails and, because of its low position, it has little mutual induction to the two track rails. Consequently, the high inductor HC is particularly efiective for inductively receiving an electromotive force in response to communication current flowing in the rails in multiple, and the low inductor LC is particularly effective for inductively receiving an electromotive force in response to communication current flowing in the line conductor L. It follows that at localities where no line conductor L is provided in the trackway, the receiving circuit of vehicle V is elfective through the medium of the high inductor HC, and at localities where a line conductor L is provided and communication current flows therein the receiving circuit is effective through the medium of the low inductor and to a lesser degree through the high inductor 1-10. I have found that the best arrangement to take care of all conditions is to use the two inductors HC and LC in series.

As set forth hereinbefore, the switching apparatus SA is operative to render either the transmitting apparatus or the receiving apparatus active and it may be operated either manually or automatically. As a result, receiving and sending may be accomplished by the equipment of vehicle V.

To accomplish two-way communication between the vehicle V and a remote location such as, for example, the locomotive of the freight train to which the caboose is attached, the locomotive is provided with communication equipment similar to that described for vehicle V.

In describing the operation of the apparatus, I shall first consider the vehicle V as operating over a stretch of railway where the line conductor L is provided. Under this condition, and assuming the crew of vehicle V desires to telephone to a remote point such as the locomotive of the train to which the vehicle is attached, the transmitting apparatus TA is rendered active to supply communication current to the sending circuit and as a result communication current flows in the rails in multiple from the vehicle and also flows in the line conductor L. To receive current on the vehicle V, the receiving apparatus RA is rendered active and current is picked up from the track rails through the medium of the high inductor coil HC, and from the line conductor L through the medium of the low inductor coil LC, the combined energy being applied to the receiving apparatus RA. In localities where the line conductor L is not provided, the operation is the same as described above except for the fact that substantially no current is received through the medium of the low inductor coil LC. The inductor coil LC may be arranged in two portions which are mounted at an acute angle with the horizontal plane, and their induction to the track rails in parallel reduced to practically zero.

Although I have herein shown and described only certain forms of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. Apparatus for communication with railway trains comprising, a conductor extending along the railway midway between the track rails, circuit means at each of a plurality of selected locations to connect the conductor with ground, transmitting apparatus mounted on a vehicle of a train and operative to supply a communication current, a sending circuit associated with said apparatus and effectively coupled with the track "rails and with said conductor to cause communication current to flow in the rails in multiple and return through the ground and to also flow in said conductor and return through the ground, receiving apparatus responsive to the communication current, and a receiving circuit associated with the receiving apparatus and including a first inductor disposed for inductive relation with the track rails and a second inductor disposed for inductive relation with said conductor.

2. Apparatus for communication with railway trains comprising, a conductor extending along the railway midway between the track rails, circuit means at each of a plurality of selected locations to connect said conductor with ground, reactance means at each of said locations connected with said conductor to reduce the characteristic impedance of the conductor for a predetermined communication current, transmitting apparatus on a vehicle of a train and operative to supply said communication current, a sending circuit associated with said apparatus and eifectively coupled with the track rails and with said conductor to cause communication current to flow in the rails in multiple and return through the ground and toalso flow in said conductor and return through the ground, receiving apparatus responsive to the communication current, and a receiving circuit associated with the receiving apparatus and including a first inductor disposed for inductive relation with the track rails and a second inductor disposed for inductive relation with said conductor.

3. Apparatus for communication with railway trains comprising a conductor extending along the railway midway between the track rails, circuit means at each of a plurality of selected 10- cations to connect the conductor with ground, transmitting apparatus operative to supply a communication current, a sending circuit associated with said apparatus and effectively coupled with the track rails and with said conductor to cause communication current to flow in the rails in multiple from the point of induction and return through the ground and to also cause current to fiow in said conductor from ground, receiving apparatus mounted on a vehicle of a train and responsive to the communication current, and a receiving circuit associated with the receiving apparatus and including a first and a second inductor, said first inductor mounted above the body of the vehicle and in a vertical plane to link a horizontal magnetic field transverse to the track rails and said second inductor mounted below the center of the vehicle for inductive relationship with said conductor. r

4. Apparatus for communication with railway trains comprising, a conductor extending along the railway midway between the track rails, a circuit network at each of a plurality of selected locations to connect the conductor to the rails in multiple to provide a ground electrode for the conductor, transmitting apparatus mounted on a vehicle of a train and operative to supply a communication current, a sending circuit associated with said apparatus and effectively coupled to the track rails to cause communication current to fiow in the rails in multiple from the vehicle, said sending circuit disposed for inductive relationship with said conductor to cause communication current to flow in the conductor and return through the ground, receiving apparatus mounted on a vehicle of the train and responsive to the communication current, and a receiving circuit associated with the receiving apparatus and including a first and a second inductor, said first inductor mounted above the body of the vehicle in a vertical plane to link a horizontal magnetic field transverse to the track rails and said second inductor mounted below the center of thevehicle for inductive re lation with said conductor.

5. Apparatus for communication with railway trains comprising, a line conductor mounted on the track ties midway between the track rails, circuit means at selected locations to connect the line conductor with ground, transmitting apparatus on a vehicle of a train operative to supply a communication current, a sending circuit associated with said apparatus and connected to two spaced wheels of the vehicle to cause communication current to flow in the track rails in multiple, said sending circuit disposed on the vehicle in inductive relationship with said line conductor to cause communication current to flow in the line conductor and return through the ground, receiving apparatus mounted on a vehicle of the train and responsive to the communication current, a receiving circuit associated with the receiving apparatus and including a first and a second inductor, said first inductor mounted on the roof of the vehicle and in a vertical plane to link a horizontal magnetic field transverse to the track rails and said second inductor mounted under the center of the vehicle in close inductive relationship with said line conductor.

6. Apparatus for communication with railway trains comprising, a. line conductor mounted on the track ties midway between the track rails, a circuit network at each of a plurality of selected locations and including a resistor connected across the rails, impedance means at each of said locations to connect said line conductor with the mid terminal of the resistor, said impedance means effective to reduce the characteristic impedance of the conductor for a predetermined communication current, transmitting apparatus on a vehicle of a train and operative to supply said communication current, a sending circuit associated with said apparatus and mounted on the vehicle in inductive relation with the line conductor to cause communication current to flow in the conductor and to ground at said locations, receiving apparatus mounted on another vehicle of the train and responsive to the communication current, and a receiving circuit associated with the receiving apparatus and including inductor means mounted under the center of the associated vehicle substantially midway between the forward and rear vehicle trucks to inductively receive current from the line conductor and to avoid picking up noise energy.

'7. Apparatus for communication with railway trains comprising, a line conductor mounted on the track ties midway between the track rails, a first resistor at each of a plurality of selected locations and connected across the track rails, two condensers at each of said locations serially interposed in the flco'nductor, said condensers proportioned to reduce the characteristic impedance of said conductor for a predetermined communication current, a second resistor at each of said locations connected between the mid terminal of the condensers and the mid terminal of the first resistor at the same location, said second resistor proportioned to substantially reduce the characteristic impedance of the line conductor, transmitting apparatus on a vehicle of a train and operative to, supply said communication current, a sending circuit associated with said apparatus and mounted on the vehicle in inductive relation with the line conductor to cause communication current to flow in the conductor and ground, receiving apparatus mounted on the vehicle responsive to the communication current, and a receiving circuit associated with the receiving apparatus and including an inductor mounted under the center of the vehicle in inductive relation to said line conductor.

PAUL N. BOSSART. 

